While the existence of a familial aggregation of seizures and epileptic syndromes has been well established, a need for more definitive studies that address the nature of the factors responsible for the observed pattern of familial aggregation clearly exists. Twin and twin kinship studies provide extremely powerful tools for measuring the importance of genetic influences on a trait, as well as, differentiating between alternative explanations for observed patterns of inheritance. The objectives of the proposed study are to determine the degree to which genetic factors play a significant role in the etiology of febrile seizures and epilepsy and to ascertain the extent to which maternal effects contribute to the predisposition to these disorders utilizing information collected from affected and control twin pairs and twin kinships who were ascertained through the Virginia or Norwegian Twin Registries. These population-based panels will provide the largest sample of affected twins that has been studied to date. A preliminary survey of the health history information available on registry members has indicated that there are currently 210 twin pairs reporting epilepsy or febrile seizures available for study in Virginia along with 320 pairs in Norway. In addition, 403 kinships in which febrile seizure is reported in the offspring of twins are included in the Norwegian panel, along with, an estimated 160 in the Virginia group. Both twin registries will be resurveyed for the occurrence of seizure disorders in twins using a questionnaire specifically developed or this purpose. Classical twin studies will be used to determine the role which genetic factors play in the etiology of seizure disorders. Case and control twin pairs will be evaluated to examine the effects of demographic variables on the incidence of the traits under study. Finally, twin kinship studies will be used to detect the influence of maternal effects on the occurrence of seizure disorders.